Road structure and process of making



' Nov. 29; 1927.

J. s. BURDGE ROAD STRUCTURE ANDPROCESS OF MAKNG original Filed Apri/1 5. 1920 esame Nov. 29, 1921.

' uNurso-sfrArias.I

VP .lirEN'r oFFlc,

'EFFERSUN S. BURDGE, O HUNTINGTON PARK, CALIFORNIA, ASSIGNOR TO WARREN BROTHER# COMPANY, F BOSTON. MASSACHUSETTS, A CORPORATION 0F 'WEST VIRGINIA.

'rllnl In. 1,390,194, Bhd eptem'ber 8, 1921, Serial I6. 371,406. led April 5, 1920.

reissue led September 7, 1823. Serial lo. 661,@32.

'.iflle present invention relates to the propavements, and has for its object the x tion of roads of improved perma- F nen e, stability, and. wear-resistance.

in 'preparing roadsfacoordin to the prescnt invention, 'a suitablelfoun ation is first prepared in any approved manner and of wearing surface, this lower portion being lli- 'crashed rock or slag, crushed or uncrushed` temperature of 350 F.,

preferably composed of the following materiels in approximately' the following proportions:

Coarse aggregate, which may be either rel. paing a two-inch screen, but retained. by a one-fourth inch screen. 45 to 60%. Medium aggregate, which may be either 'rushed rock or slag, crushed or nuncrushed revel, or sand passing a one-fourth inch af aen and retained by a one-tenth inch screen, to.15%.

Fine aggregate, which may be either crushed gravehslag or rock, or sand passing a one-tenth inch screen, to 38%.

Bituminous cement. 5 to 7%. The bituminous cement employed in this lower portion should be of such a character that it will become thoroughly molten at a amount stated above is found to be entirely suicient for producing the structural, Weight sustaining, 'displacement resisting portion. -Upon this isplaced the wear-re- 0 sisting or finishing portion.

M and plastic.

but generally a depth of from 1 to 3 inches Preferably7 the materials forming the lower portlon are previously thoroughly mixed and applied to ,the roadway while hot, so that th'e bituminous cementwill be soft l The thickness of the layer 'forming the .first portion will depend upon the character of the foundation upon which it is laid and the amount and the.. character of the traflic to which it is to besubjected,

is to be preferred. It should contain about 50% or say 45 to 66%Iof coarse aggre ete, and .it is advisable that the largest'o the on of permanent and wear-resisting` or less, andl the.

ROAD STRUCTUBEAAD PROCESS 0F MAKING.

.Application for pieces of the mineral aggregate in the structural portion should he of a, size equal to v.about one half of the depth or thicknessof the completed wearing surface. The aggregate, stone. gravel, or slag, sand, etc., em*

ployed in the lower portion are preferably,

heated to about 200 to 400 F., and mixed roughly whereupon the bituminous cement is .added preferably in a molten condit1on, and the mass then mechanically mixed while at a temperature at which the bituminous cement is liquid or semiliquid until a uniform mixture is produced, and this mixture isthen spread preferably while hot upon the foundation to give the desired depth, andr with its surface true to grade and con-` tour It is usually ,advisablejnot to compress or roll the lower portion at this stage.

The finishing or wear-resisting portion isk then spread-on the structural portion and this finishing portion consists of natural bituminous or asphaltic sand or rock. reduced to a granular conditionvby either pulverization or heat, that is to say. mineral matter which is naturally impregnated or coated with bituminous material, which natural bituminous rock 'or sand is known to possess remarkable properties of resistance to abrasion. such as is produced by tratiic, but'whi ch by itself. is open to the objection of lackor rut'tng under traic.

l'n the production of the finishing portion I preferably add on top of the uncompacted lower portion a thin mat` of this material, this being preferably applied while the lower ing stability and resistance to displacement portion f is still hot, that is to say, beforel the bituminous cement therein has hardened or set. There are various kinds of natural bituminous or asphaltic sand or rock. which may be employed for this upper course, but it is preferable to use a material, the par,-

lticles of which are thoroughly impregnated with pure asphaltum in such amount that 10 to 20% by weight -of the material is soluble in'carbon disulfid. vIf vthe natural bituminous or asphaltic sand or rock con- 'tains a substantially greater or lessA percentage of the soluble material than above specified, then it is advisable, for example during the grinding. pulverizing or hea-ting operation, to add either a sulicient quantity of tine y"sand or crushedy stone screenings or will depend to add bituminous cement or a thick asphaltic oil in liquid form to secure a product within the range `above stated. b'viously, the sand, crushed stone, bituminous cement or oil could be added at any'other convenient i to spread the same at ordinary atmospheric tem erature, the spreading boing' performed AWlii e the material of the lower portion is still hot, as above stated.

. The entire structure is then compressed as a unit, preferably by means of a self-pro polled' heavy roller until the finished wearresisting portion and the lower structural portion become thoroughly vcompacted and completely united with each other. The

operation of compression causes thenatural bituminous or asphaltic sand or rock to become semiplastic orA plastic, due in part to kheat developed by friction between the component particles of the structure during theA process of compression and 'in part to the transmission'oi heat from the previously heated material. forming the structural por tion. `/Vhile in `this plastic condition, the grains of: the upper portion are found to thoroughly unite with each other and to be thoroughy bonded to tlielou'er structural n portion.

After the finishing portion has been thoroughly compressed while it is still in a slightly' plastic condition light sprinkling of crushed v stone., Portland cement, sand,

gravel or pulverized stone or slag may, it desired, be uniformly applied and rolled into lthe same. A

During the rolling or compacting operation"thc fine material. -constituting the top portion will enter the voids or cavities in the upper part of the lower portion to some extent thereby producing a very eii'ective bondingy of the upper and lower'portions. It is to be understood, however, that considerable of the upper ortion remains above the coarse materiale the lower or structural portion.l The `amount depending upon the condition oi the lower portion.` andthe depth of the material rused for the jupper portion;

lGil

The' annexed drawing illustrates a cross section of a road eonstructedin accordancewith aq preferred embodiment of the present invention. 'In said drawing, l represents the foundation, 2 represents aV suitable lower or structuralportion, this being composed of coarse aggregate, 3; medium aggregate, `4;

and fine aggregate 5; proportioned prefer ably above described and mixed `with from 5 to 7% ot' bituminous cement, 'and 6 represents the surfacing or wear-resisting portion. the lines 7 and 8, in which the two layers become thoroughly blended and united and bonded together, by compression. In the surface may be located the hard fine material i), i desired.

I u1u, ot course, familiar with bituminous or asphaltic concrete pavements, but I believe that the use ot' natural bituminous or asphaltic sand or rock, applied as above specified, as an abrasioli-resisting surfacing, is an entirely new addition tothe road building art.

W'hile the lower structural ,portion de scribedabove, has been shown by tests, which have been made, to be especially suitable vfor use in my invention, l do not restrict myself to this particular lower structural portion, because any other bituminous mix-- ture or bituminous coated road body which has sutlicient weight-sustaining and dis placementdesisting strength may .also be usedl as the lower structural portion, therefore the applcatiobf such finely divided (granular or piilvr"ized),'nat1iral asphaltic,

or bituminous rock or sand to any suitablel bituminous mixture or bituminous coated road body, by the method herein described A is within the scope of my invention.

As stated above, it is advisable to apply the wear-resisting upper portion u on the ,lower structural portion, -while the -atterv is still in a heated condition (say, at between 200 and 400 E). However, I do not restrici myself to this temperaturevrange in the lower structural portion at the time of application of the material to constitute the wear-resisting portion andai; the time of the i compression of the pavement, since the primary object is to facilitate the roper blendand bonding together of tllie upper and lower port-ions of the pavement, during compression, f 1

This bonding can be obtained when the bituminous cement in the lower structural portion is sufficiently hot and plastic to' blend with the bituminous or asphaltic eement. of the fine material constituting the ,upper portion. Accordingly' any tempera tureat which the bituminous cement in the lower Astructural portion is plastic orfliquid (i. e.. Vany temperature at which it can ilow) is to be considered as suflicientlly, elevated to c me 'within the spirit of the present ,invenw ti n. This temperature, will of course, dem pend to a considerable extent upon the charu acter of the bituminous cement present in the lower or structural portion.

I claim:

1. The improvement in road-building, which compr1es-the step of applying natl call attention to the zone between' ural bituminous or asphaltio sand or rock in a granular. condition in such amount as to leave a thin Wear-resisting surfacing portion composed-essentially of such ii'iaterial to a manufactured 'bituminous or asplialtic coiicrete pavement structure, while the latter is 'still hot. f

2, The improvement iii road-building which comprises the steps ot applying a layer of cold, natural bituminous orasphaltic sand or rock in a granular condition in such amount :is4 to leave a thin wear-resisting surfacing portion composed essentially-of such -material to a lower structural portion oi a manufactured bituminous yor asplialtic concrete parement structure, wnile the lattei is hot, and then 'compressing thestructure,

` whereby said upper portion becomes heated and' plastic during the process of laying, over' and compression into the heated, lower structural portion.

3. In the manufacture of a road. the process which comprises first spreading a structural portion comprising coarse and fine mineral aggregate and bituminous ce` ment, such spreading being effected While the material is suiiiciently hot for the cement to be plasticrthen spreading thereupom.

Without previous compecting, arelatively thin portion of natural bituminous rock o r sand, in a graiiuiarcondition, and then compacting `the compound structure While the lower layeris stili hot.

i 4. In the manufacture of a road, the im-` provement which comprises spreading on a hot lower portion, a cold natural bituminous rock or sand, ina granular condition, and then compacting while the heat of the lewe portion is retained in the mass.

5. .A process of building a road structure which comprises spreadingand grading a hot road-building material as a loose non-` compacted body, then spreading thereupon a cold finely divided natural bituminous rock `or sand, such second mentioned product being applied while the i'irst mentioned materialn is ina hot noncompacted condition, and

. then ycompressing the entire structure, to

effect a blending and densiticatiomof the constituent parts of the said road structure,

While the cold top material becomes heatedand rendered plastic by the. -lieat contained in the hot lower material.v

6 A process of buildingffa road structure.

which comprises spreading and grading a. bituminous road-building material as a loose non-coni acted body at a' temperature at which t e bituminous' cement therein is luent, then spreading thereupon a. finely divided natural bituminous rockv or sand, and

.then compressing the entire structure to effect a blending and densication-of the constituentpiirts'ofA the said road structure. 7, 'A process of building a road structure 'y which comprises a spreading bituminous road-building material, then spreading thereupon a\ finally divided natural bituminous rock or sand in such amounts as to leave a surfacing portion consisting essex tiall'v thereof and then compressing tlie entire structure to etl'ect a blending and densif iii-ation of the constituent parts of said road structure.

i S. ln thii construction of roads, the herein described improvement which comprises spreading con'iininutcd natural bitui'ninous rock or and upon :i lower structural portion,

and tlieii compressing the saine, botli of said opcratiom4 beingr performed while said lower structural portion is atA a temperature at which the bitumen content of such coiniiiinuteil material can dou'.

9. A. composite road'structure, comprising a lower structural portion and an upper .wear-resisting portion,l such lower portion comprising l Perczezit:y Coarse mineral aggregate 45 110.60 Medium .mineral aggregate l@ to i l@ inch size 10 to l5 Fine mineral aggregate less than {U- incli size 20 to 38 Bituminous cement T 5 to 7 and such upper portion consisting essentiaily of compacted natural` bituminous rock or sand, containing 10 to 20% of bitumen soluble in carbon disuliid.

10. A complete pavement Wearing surface having a lower structural portion consisting essentially of manufactured bituminous or Hitt asphaltic concrete or macadam or mortar,

and an upper warresistin surfacing por'- ltion consisting essentially vo natural bituminous rocker 'bituminous sand, such upper portion being more plastic than such structural portion, the two portions being blended together and united with each other,and a hardv finely divided material incorporated into the surface of the said upper portion.

11. A road structure process ofthe charlli-5 acter' described, consisting in applying upon a compacted foundation a hot compound of 4three graded bodies of aggregate, relatively coarse, medium and fine with respect to each other, ,the coarse aggregate and the tine ag gregat'e being proportionately greater in -qnantity than the medium aggregate, the

said aggregate being Acour-pounded. with bin tuminous cement vcomprising live to seven per cent of the compound and adapted to melt fully below 350 F., the said aggregates.-

andcement compoundrbeing applied to the foundation without rolling, and a top wearresisting portion of natural bituminous sand orrock in granular condition, they whole lie-- ing finally compacted.l Y.

12`A road structure process ofthe charact'er described, consisting in applying u n a. compacted foundation a hot compoun of ,below 3500 three gra-ded bodies'of aggregate, relatively coarse, medium and fine with respect to each other, the coarse aggregate and the fine aggregate being proportionately greater. in quantity than the medium aggregate, ille coarsel aggregate being yproportionately greater in quantity than the line aggregate, the said aggregates being compounded with bitulninolis cement adapted to melt fully F., the said aggregates and eement compound being applied to the foundation without rolling, and a to wear-resisting portion olf' natural bltnnnnons sand or rook in granular condition, the whole being finally compacted.

13; A road Structure process of tbe character described, consisting in applying npon a compacted road-foundation a bot, coinpound of three graded bodies of aggregates,

relatively coarse, medium and line with respeel'r tol eacb other,

lJEFFERSON s. BURDGE.

the coarse aggregate .l and the fine aggregate being proportionate-A 

